The reasons why the lips inexplicably swell up are as follows: 1. When periapical inflammation occurs in teeth, a large amount of inflammatory secretions accumulated at night break through the gums, reach the vestibular sulcus, and extend to the lip gap, causing obvious swelling of the lips, even accompanied by edema of the jaw and face. 2. When suffering from allergies, contact with drugs or cosmetics, angioneurotic edema occurs, leading to sudden abnormal swelling of the lips. 3. When autonomic nerve, When vasoconstriction disorder occurs, sudden edema of the upper and lower lips, accompanied by exudate, occurs granulomatous labyrinthitis, and sometimes other parts of the face, such as the nose, periorbital area, and cheeks, also appear obviously swollen.